The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to etch film on a substrate such as a semiconductor wafer. The substrate processing systems typically include a substrate processing chamber, a gas distribution device and a substrate support. During processing, the substrate is arranged on the substrate support. Different gas mixtures may be introduced into the substrate processing chamber and radio frequency (RF) plasma may be generated to activate chemical reactions. The RF plasma may be an inductively coupled plasma (ICP) or a transformer coupled plasma (TCP). The ICP or TCP may be provided by a plasma source as a result of charging one or more coils. The plasma source includes an upper portion of a substrate processing chamber and the one or more coils.
A chamber member of an ICP source may be cylindrically-shaped or dome-shaped. A chamber member of a TCP source may be flat-shaped. A cylindrically-shaped chamber member of an ICP source has coils located around a circumference of the chamber member. A dome-shaped chamber member of an ICP source is spherically-shaped and has coils disposed above the chamber member. A flat-shaped chamber member of a TCP source includes a flat circular dielectric window above which coils are mounted.
Plasma sources with cylindrical, dome and flat shaped chamber members have associated disadvantages. The disadvantage of the cylindrically-shaped chamber member is that all of the corresponding coils are located around the circumference of a cylinder, which does not allow for adjusting a radial plasma density from a center (e.g., vertical centerline extending through a center of the cylindrically-shaped chamber) to an outer circumferential edge of the cylindrically-shaped chamber member.
The dome-shaped chamber member may have a center mounted coil and an outer mounted coil. The center mounted coil may be located near a top and center of the dome-shaped chamber member. The outer mounted coil may be located further down on and near a perimeter of the dome-shaped chamber. The disadvantage of the dome-shaped chamber member is that a larger distance exists between the center mounted coil and a center of a substrate as compared to a distance between the outer mounted coil and the substrate. This longer distance in the center of the corresponding plasma source can result in longer residence times for plasma species generated in the center versus the outer edge. This affect is more pronounced when high pressure gases are supplied and/or when electronegative gases are supplied due to localized areas with high density plasma.
The disadvantage of the flat-shaped chamber member is that the corresponding coils are typically located a considerable distance away from the plasma due to a thick dielectric window (e.g., 1-2 inches in thickness). The dielectric window is thick to withstand mechanical forces generated by a difference in pressure across the dielectric window. The physical separation between the chamber member and the plasma reduces efficiency of the corresponding TCP source because mutual inductance between the coils and plasma is decreased. This results in increased current flowing through the coils and increased copper loss (i.e. increased magnetic field loss). The further away the coils are from an interior chamber region of the chamber member the more magnetic field loss and thus the more current needed to provide the required magnetic field in the interior chamber region.